1. Field of the Invention
The present invention relates to improvements in prostheses of the upper end of the humerus, of the type comprising a stem which is anchored in the humeral canal and a semi-spherical cap adapted to cooperate with the glene of the shoulder.
The prosthesis according to the invention associated with a prosthetic glene allows surgical treatment in particular of degenerative disorders of gleno-humeral arthrosis, but also that of other disorders. In isolated manner, the humeral prosthesis according to the invention is intended for broad indications such as cephalo-tuberositary fractures not accessible for conservative surgery, but also for any painful syndrome of the shoulder connected with an isolated destruction of the humeral head (osteonecroses, etc.).
2. History of the Related Art
Of course, prostheses intended for such treatments are already known, such as so-called NEER ones. However, such a prosthesis is monobloc, with the result that a large number of implants must be kept in stock in order to respond to the needs of the various patients. Moreover, these prostheses present one single size of stem and semi-spherical cap, the latter not being able to be offset as is necessary in certain cases. Moreover, this cap has a fixed inclination and it does not satisfactorily cover the plane of section of the end of the humerus, with the result that the bone must be adapted to the prosthesis, with all the anatomical consequences that this involves.
According to Swiss patent 507 704, a prosthesis stem is also known which comprises at one of its ends a flange provided with a bearing surface. The flange is intended to rest on the remainder of the osseous part.
A pivot issues from the flange, creating an angle of inclination with respect to the bearing surface. The pivot is preferably conical and includes on its periphery retaining means such as ribs, teeth, projections or the like.
On this prosthesis stem may be fixed different ball-and-socket joints which are all provided with a neck having a variable inclination. Fixation is effected by the pivot and the retaining means. The use of a plurality of ball-and-socket joints makes it possible to define the most favorable angle of inclination, the angle of retrotorsion and the lateral offset of the semi-spherical cap.
Such a prosthesis presents certain drawbacks concerning the flange which is provided with a bearing surface intended for the flange to rest on the remainder of the osseous part, preventing optimum hold of the prosthesis in the metaphysis and clearly reducing the spatial displacement of the cap.